1. Field of the Invention
The present invention relates to a force sensor for controlling polishing pad pressure and, more particularly, to an apparatus for controlling the force exerted by a polishing member upon a material being polished.
2. Description of the Prior Art
The present invention relates to the manufacture of rigid computer memory discs of the type which are used with a memory apparatus of a computer for storing data thereon. These discs are typically made of an aluminum alloy, having inner diameter of 1.576 inch, an outer diameter of 5.118 inches, and a thickness of 0.075 inch. The opposed surfaces of the discs are coated with a magnetic coating for memory use.
In the manufacture of such discs, as well as in the manufacture of other products, equipment is used to impart a super-fine finish to the disc surface. This equipment usually includes a polishing wheel or tape having in it a grit for metal removal, thereby causing the polishing action, with the grit held by a binder material forming the wheel or adhered to a plastic film forming the tape. The wheels are often called "pads" and these pads contact the disc face-to-face, rather than on edge. Moreover, pads are generally used in pairs, contacting both sides of the disc simultaneously. The intent is to exert equal forces on both sides of the disc so that the forces balance each other and do not distort the disc being polished. In operation, the pads are rotated, creating a polishing action on the disc face and the disc is also rotated, causing an even polishing action over the whole disc face.
A significant drawback to existing apparatus of this type is in the inability to adequately control the force exerted on the disc by the rotating pad. The apparatus presently used for applying force through the rotating pad to the disc is typically spring-loaded, free sliding shafts, where the motion of the sliding shaft compresses a spring which in turn applies the force to the pad. Another apparatus applies air pressure to a gland which acts over an area of a flange, creating a force on the pad, in effect acting as an air spring In both cases, the force exerted on the disc by the rotating pad cannot be controlled and, most importantly, it is not possible to maintain an equal force on each side of the disc. With unequal polishing forces, the disc being polished is often distorted.